This program encompasses a broad laboratory and clinical research program aimed at clarifying the basic mechanisms involved in heart attack (acute myocardial infarction) in man and in experimental models, with the goal of providing a better understanding of the natural history of myocardial infarction, assessing the effects of surgical and medical therapy in patients with coronary heart disease (angina pectoris, heart attack, dysrhythmias, and cardiac failure), and devising new forms of therapy for these conditions. The experimental models employed range from in vitro studies, ischemia in tissue and organ culture, acute experiments in a variety of animal preparations, to studies in chronically instrumented, unanesthetized animals and subhuman primates. Both the clinical and laboratory research programs bring to bear such techniques as hemodynamic and radiographic analysis, radioisotopes, echocardiography and other noninvasive methods, new ultrasonic devices, measurement of serum enzymes and isoenzymes, study of the andrenergic nervous system, basic biochemical measurements in the heart muscle and electronmicroscopy to bear on the solution of these problems.